In the art of optical instruments, it is known to scan a surface to be imaged with a small light source, collect the light reflected from the illuminated spot and direct it to a detector which provides an output signal varying in time in correlation with the scanning of the illuminated spot across the surface. The detector output can be stored in a permanent storage medium or provided directly to a scanning display device, such as a television raster or a cathode ray tube display. By synchronizing the scanning operation of the illuminating source with the scanning of the display signals, a two dimensional image is produced.
One such instrument is a scanning ophthalmoscope which produces an image of the fundus of the eye. It has been found that the use of a laser light source provides improved imaging in an ophthalmoscope. A laser scanning ophthalmoscope is described in U.S. Pat. No. 4,213,678.
In a device as described in the noted patent, the entrance pupil for the scanning laser beam has a small cross sectional area within the pupil of the eye, typically 0.8 mm in diameter, whereas the exit aperture for the reflected light is the overall pupil of the eye, which typically is nine mm in diameter. The detector is placed in a plane conjugate to this exit aperture.
An improved technique is described in pending U.S. application Ser. No. 876,230 filed June 19, 1986 and U.S. application Ser. No. 876,231 filed June 19, 1986.